The locking screw mechanism of the present invention is described for locking a magazine that holds strips of integrated circuit packages in a solder plating machine during manufacture of integrated circuit packages. However, the locking screw mechanism of the present invention may advantageously be used for locking any other object in place, as would be apparent to one of ordinary skill in the art from the present description herein.
Referring to FIG. 1, a magazine 12 is locked into place in a solder plating machine during manufacture of integrated circuit packages by four locking screw mechanisms including a first locking screw mechanism 14, a second locking screw mechanism 16, a third locking screw mechanism 18, and a fourth locking screw mechanism 20. The magazine 12 holds a first strip 22, a second strip 24, and a third strip 26 with each of the strips 22, 24, and 26 comprising a plurality of integrated circuit packages. For example, the first strip 22 is comprised of a first integrated circuit package 102, a second integrated circuit package 104, and a third integrated circuit package 106. A magazine typically includes more than three strips. For example, the magazine 12 typically holds eighty strips stacked within the magazine 12. However, the magazine 12 of FIG. 1 includes the three strips 22, 24, and 26 for clarity of illustration.
Each of the strips 22, 24, and 26 is comprised of a plurality of integrated circuit packages during manufacture of the integrated circuit packages. FIG. 1 shows a side view of the strips 22, 24, and 26 stacked within the magazine 12. Referring to FIG. 2 for example, a top view of the first strip 22 shows a top view of the first integrated circuit package 102, the second integrated circuit package 104, and the third integrated circuit package 106. A strip typically includes more than three integrated circuit packages, but the strips 22, 24, and 26 of FIGS. 1 and 2 include three integrated circuit packages for clarity of illustration.
Each of the integrated circuit packages on a strip has a plurality of leads. Referring to FIG. 3 for example, the first integrated circuit package 102 includes a first lead 112, a second lead 114, a third lead 116, and a fourth lead 118 on one side of the integrated circuit package 102. The first integrated circuit package 102 also includes a fifth lead 120, a sixth lead 122, a seventh lead 124, and an eighth lead 126 on the other side of the integrated circuit package 102. An integrated circuit package typically includes more than eight leads, but the integrated circuit packages 102, 104, and 106 of FIGS. 2 and 3 include eight leads for clarity of illustration.
Referring to FIG. 1, the strips 22, 24, and 26 of integrated circuit packages are stacked within the magazine 12, and the magazine 12 is clamped to a solder plating machine by the locking screw mechanisms 14, 16, 18, and 20 to plate the leads of the integrated circuit packages with solder which typically is comprised of tin (Sn) and lead (Pb). Referring to FIG. 4, a side view of one of the locking screw mechanisms 14, 16, 18, and 20 of the prior art illustrates a screw head 150 and a screw nut 152 that clamp the magazine 12 in place in the solder plating machine. (Elements having the same reference number in FIGS. 1 and 4 refer to elements having similar structure and function.) Referring to FIGS. 1 and 4, the magazine 12 is placed between the screw head 150 and the screw nut 152.
The screw nut 152 is then threaded about a screw shaft 154 to move the screw nut 152 toward the magazine 12 (in accordance with the right hand rule as known to one of ordinary skill in the art of mechanics). Referring to FIGS. 4 and 5, the screw nut 152 is threaded about the screw shaft 154 toward the magazine 12 until the screw nut 152 contacts and presses the magazine 12 against the screw head 150 such that the magazine 12 is firmly held between the screw head 150 and the screw nut 152. (Elements having the same reference number in FIGS. 1, 4, and 5 refer to elements having similar structure and function.)
Referring to FIG. 5, the screw head 150 has a first contact surface 156 and the screw nut 152 has a second contact surface 158. Referring to FIGS. 1 and 5, when the magazine 12 is clamped between the screw head 150 and the screw nut 152, the magazine 12 makes contact with a portion of the first contact surface 156 of the screw head 150 and with a portion of the second contact surface 158 of the screw nut 152. For example, FIG. 6 illustrates the second contact surface 158 of the screw nut 152 that surrounds the screw shaft 154. The portion of the second contact surface 158 of the screw nut 152 that makes contact with the magazine 12 (when the magazine is clamped between the screw head 150 and the screw nut 152) is shown as the shaded contact area 160. (Elements having the same reference number in FIGS. 1, 4, 5, and 6 refer to elements having similar structure and function.)
Referring to FIG. 1, the magazine 12 holding a plurality of strips 22, 24, and 26 of integrated circuit packages is clamped to a solder plating machine by the plurality of locking screw mechanisms 14, 16, 18, and 20 for plating the leads of the plurality of integrated circuit packages with solder during manufacture of the integrated circuit packages. After this solder plating process, the magazine 12 is released from the solder plating machine by loosening the plurality of locking screw mechanisms 14, 16, 18, and 20. The magazine 12 holding the plurality of strips 22, 24, and 26 of integrated circuit packages is then transferred to another station for further processing of the integrated circuit packages in the manufacture of the integrated circuit packages.
Referring to FIG. 5, for loosening the locking screw mechanism, the screw nut 152 is dethreaded about the screw shaft 154 away from the magazine 12 (in accordance with the right hand rule as known to one of ordinary skill in the art of mechanics). The force required to turn the screw nut 152 for initially dethreading the screw nut 152 away from the magazine 12 (while the magazine 12 is clamped between the screw head 150 and the screw nut 152) is determined predominantly by two counter-forces. A first counter-force is the frictional force between the threading of the screw shaft 154 and the threading within the screw nut 152.
Referring to FIG. 6, a second counter-force is the fictional force in the contact area 160 between the screw nut 152 and the magazine 12. When the magazine 12 is clamped between the screw head 150 and the screw nut 152, the screw nut 152 is pressed against the magazine 12 at the contact area 160. When the screw nut 152 is initially loosened, the screw nut 152 turns against the magazine at the contact area 160 with a frictional force as the screw nut 152 is turned during the dethreading of the screw nut 152 about the screw shaft 154.
The force required for loosening the screw nut 152 must overcome the above described frictional counter forces. In the prior art locking screw mechanism of FIGS. 4, 5, and 6, such a force required for loosening the screw nut 152 when the magazine 12 is clamped between the screw head 150 and the screw nut 152 may be too high because of the large frictional counter forces. In particular, in the locking screw mechanism of the prior art of FIG. 6, the contact area 160 is relatively large leading to a relatively high frictional force between the screw nut 152 and the magazine 12 as the screw nut 152 is dethreaded about the screw shaft 154.
Referring to FIG. 1, when the force required to loosen the locking screw mechanism is too high, an operator during the manufacture of integrated circuits cannot easily release t he magazine 12 from the plurality of locking screw mechanisms 14, 16, 18, and 20. With such a high force requirement, the operator's hands may feel too sore in repeatedly attempting to release the magazine 12 from the plurality of locking screw mechanisms 14, 16, 18, and 20 as a large number of integrated circuit packages are manufactured during a day.
The strips 22, 24, and 26 of integrated circuit packages need to be transported from one processing site to another processing site during the manufacture of the integrated circuit packages. After processing of the strips 22, 24, and 26 of integrated circuit packages on the magazine 12 at one processing site, the magazine with the strips 22, 24, and 26 of integrated circuit packages should be released from the plurality of locking screw mechanisms 14, 16, 18, and 20 to be transported to the next processing site.
However, when the force required to loosen the locking screw mechanisms is too high, the operator is compelled to leave the magazine in place and to move the strips 22, 24, and 26 of integrated circuit packages from a magazine that remains clamped by a plurality of locking screw mechanisms at one processing site to another magazine that remains clamped by the plurality of locking screw mechanisms at the next processing site to avoid loosening the locking screw mechanisms for releasing the magazine.
Unfortunately, referring to FIGS. 2 an 3, when the strips of integrated circuit packages are handled by the operator, the delicate leads of the integrated circuit packages tend to be bent. Time is wasted in transferring the plurality of strips of integrated circuit packages from one magazine to another magazine and in fixing the undesirably bent leads of the integrated circuit packages. Thus, a locking screw mechanism is desired that requires minimized force for loosening the locking screw mechanism when an object such as the magazine 12 is clamped therein.